(NaturalNews) Atmospheric levels of the two major greenhouse gases leaped in 2007, according to a report by the U.S. National Oceanic and Atmospheric Administration. This increase is part of a wider trend of accelerating greenhouse gas emissions.

"The average [annual rise] over the last five or six years has been 2 parts per million (ppm), and that is actually steeper than it has been in previous decades," researcher Pieter Tans said. "This whole decade the rate of increase has accelerated, and we have a very clear candidate [for the cause] and that's emissions from burning fossil fuels."

While atmospheric carbon dioxide levels were only 270 ppm before the Industrial Revolution, they now stand near 390 ppm. The increase in 2007 was 2.4 ppm, or 0.6 percent, amounting to a 19 billion metric ton increase. Methane levels increased 0.5 percent, or 27 million metric tons.

Together, the two gases are thought to be the major causes of global warming. While methane has 25 times the heat-trapping effect of carbon dioxide, the significantly lower methane levels in the atmosphere mean that the gas contributes only about half as much to global warming as carbon dioxide does.

The researchers noted that while carbon dioxide levels have been steadily increasing since the Industrial Revolution, atmospheric methane concentrations had held relatively steady since 1998, after increasing for 20 years. They said this might be a warning sign that the methane trapped for thousands of years beneath Arctic soil might be escaping into the atmosphere as the permafrost melts.

The release of methane from Arctic permafrost is expected to accelerate the process of global warming, leading to still more ice melt and the release of more methane in a positive feedback loop.

"What used to be in the deep freeze is now being taken out in the warming," Tans said